The evidence for molecular intervention (almost always with positive outcome) of antioxidants in the form of phytochemicals (the ones that have been around us for millions of years) in the biochemistry that occurs in animal bodies is overwhelming as a search in the literature will tell you. I've read hundreds of papers reporting such results.
No one talks about proof in science but this is at least indicative though we have far to go.
To ignore the chemistry while waiting for epidemiologists to come to questionable conclusions seems odd to me.
Thanks to the countless variables present when people are involved, epidemiological studies are always subject to debate.
Knowing as a raw fact that carbon monoxide irreversibly combines with haemoglobin told me a long time ago that smoking is a mug's game I was likely to lose. I didn't need later 'reassurance' from epidemiology to persuade me give up.